1. Field of the Invention
The present invention relates to a polymeric fluorescent substance, a polymer light-emitting device (hereinafter, referred to as polymer LED), and a device using the same.
2. Description of the Related Art
Inorganic electroluminescence devices (hereinafter, sometimes referred to as inorganic EL device) using an inorganic luminescent material as a light-emitting material are used for example for sheet light sources as back-lights and displays such as a flat panel display and the like, however, an alternating current of high voltage has been required for light emission.
Recently, there has been reported an organic electroluminescence device (hereinafter, sometimes referred to as organic EL device) having a double-layer structure in which an organic fluorescent dye as a light-emitting layer is laminated with an organic charge transport compound used in photosensitive layer for electrophotography and the like (Japanese Patent Application Laid-Open (JP-A) No. 59-194393). Since organic EL devices have characteristics that light emissions of a lot of colors are obtained easily in addition to low voltage driving and high luminance as compared with inorganic EL devices, there have been reported a lot of trials regarding device structures, organic fluorescent dyes and organic charge transport compounds of organic EL devices [Jpn. J. Appl. Phys., 27, L269 (1988), J. Appl. Phys., 65, 3610 (1989)].
Further, apart from organic EL devices using mainly organic compounds having a lower molecular weight, polymer light-emitting devices using light-emitting materials having a higher molecular weight have been proposed in such as WO 9013148 published specification, JP-A No. 3-244630, Appl. Phys. Lett., 58, 1982 (1991). WO9013148 discloses in the Examples an EL device using a thin film of poly(p-phenylene vinylene) obtained by forming a film of a soluble precursor on the electrode and subjecting it to a heat treatment to convert the precursor into a conjugated polymer.
Further, JP-A 3-244630 has exemplified a conjugated polymers having a feature that they are themselves soluble in a solvent and needs no heat treatment. Also in Appl. Phys. Lett., 58, 1982 (1991), a polymeric light-emitting materials soluble in a solvent and a polymer LED fabricated using the same are described.
Polymer LEDs are advantageous for formation of a film having large area and reduction in cost since an organic layer can be easily formed by coating with using a polymeric fluorescent substance soluble in organic solvents, as compared with the case of vapor deposition of a material having a lower molecular weight, and the mechanical strength of the resulting film is believed to be high because of a high molecular weight thereof.
Conventionally, as the light-emitting materials used in these polymer LEDs, in addition to the above-described poly(p-phenylene vinylene), there have been reported polyfluorene (Jpn. J. Appl. Phys., 30, L1941 (1991)), poly p-phenylene derivative (Adv. Mater., 4, 36 (1992)) and the like.
In order to utilize the film-formable characteristics of a polymeric fluorescent substance by coating, there have been demanded a polymeric fluorescent substance having excellent solubility in organic solvents. To realize the practical flat panel display, there have been demanded a polymer LED having high efficiency and long.
The object of the present invention is to provide a polymeric fluorescent substance having more excellent solubility to organic solvents, a polymer LED having high performance which can be driven at high efficiency and longer lifetime using said polymeric fluorescent substance.